<template>
    <ul class="list">
        <li 
        class="item" v-for="item in letters" 
        :key="item"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @click="handleLetterClick"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        >{{item}}</li>
    </ul>
</template>
<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    data(){
        return{
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY = this.$refs['A'][0].offsetTop
    },
    computed:{
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(()=>{
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if(index >=0 && index < this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                },16)
                
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list 
        display:flex
        flex-direction:column 
        justify-content :center
        position:absolute
        top:1.58rem 
        right:0 
        bottom:0 
        width:.4rem 
        .item 
            line-height:.4rem 
            text-align:center 
            color:$bgColor
</style>